Background to fit
Resize the window, and the background image will scale to fit the new window size. Well, not the background image, actually, but an image that seems to be a background image

For best results with NN4 set the BODY tag attributes of MARGINWIDTH and MARGINHEIGHT to 0.

Based on Peter Belesis code, check: http://webreference.com/dhtml/diner/bgresize/
for a detailed explanation